Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$90.83	9.369%	$99.3399	$99.34	$99.35	$99.30
Purchase #2	$184.70	6.523%	$196.748	$196.75	$196.75	$196.70
Purchase #3	$78.37	4.789%	$82.1231	$82.12	$82.10	$82.10
Purchase #4	$81.52	3.167%	$84.1017	$84.10	$84.10	$84.10
Purchase #5	$195.67	5.867%	$207.15	$207.15	$207.15	$207.20
Purchase #6	$215.86	10.329%	$238.1562	$238.16	$238.15	$238.20
Purchase #7	$49.43	6.306%	$52.5471	$52.55	$52.55	$52.50
7 purchase totals =	$896.38		$960.1660	$960.17	$960.15	$960.10